Remote sensing of agricultural crop residue and conservation tillage

The Science Issue and Relevance
Conservation tillage is an agricultural best management practice designed to reduce the loss of soil and nutrients from farmland by protecting the soil surface from wind and rain. Adoption of conservation tillage methods by regional farmers has been identified as a priority practice by Chesapeake Bay Watershed Program partners, and a need has been identified to monitor conservation progress. Measurement of crop residue contributions to groundcover typically requires in-field sampling using beaded string or photographic methods. Remote sensing of soil surface reflectance has also been used to measure crop residue, either by contrasting the intensity of soil vs. residue reflectance in the visible and near infra-red wavelengths, or more recently by characterizing cellulose spectral adsorption features found in the short wave infra-red (SWIR) wavelengths. Our research objective is to use satellite imagery to map crop residue on agricultural fields, and develop methods for distinguishing among plow (0-30% residue), conservation (30-60% residue), and high residue management (60-100% residue) tillage strategies.

Methodology for Addressing the Issue
Crop residue is best measured in springtime, following tillage and planting of the summer crop. There is a brief window of opportunity for remote sensing after the green winter landscape has been transformed by tillage, and before summer crop vegetation covers the soil surface and interferes with the visibility of residue. In the spring of 2015 we worked with an Eastern Shore farmer to measure crop residue shortly after springtime field management was complete. Reflectance from a May 15th Worldview 3 SWIR image showed strong correlation with in-field measurements of percent residue cover on fields with little green vegetation. Results showed capability for mapping crop residue based on characterization of cellulose adsorption with SWIR indices.

Future Steps Worldview 3 SWIR residue mapping will be used to increase scale and calibrate analysis of Landsat imagery collected on similar dates. On-farm sampling and Worldview 3 imagery collection will be repeated this spring, thus expanding our sampling range to identify when the residue signal becomes obscured by green vegetation.